The present invention relates to an individually selective calling receiver for use in a mobile communication system or the like.
An individually selective calling receiver is carried by a person who is outdoors or away from his desk and receives a calling signal sent by means of an electric wave to respond to it. In such a receiver, different identification numbers are assigned to a plurality of receivers, respectively, and a transmitter sends the identification number assigned to a specific receiver to selectively call the receiver. Accordingly, in the individually selective calling receiver, reception sensitivity is most important and even when a user of the receiver is present in any area, it is desirable to be able to receive a call.
In the conventional individually selective calling receiver, however, an interval of transmission time is about five minutes with transmission for two minutes and a pause of transmission for three minutes repeated. However, there is a case where an electric wave is attenuated behind a building or within a building and a field intensity of the electric wave does not reach reception sensitivity. Thus, there is a problem that the user does not understand whether it is possible to receive a call in his place during a time domain for the pause of transmission.
A technique to solve the above problem is disclosed in Japanese Patent Unexamined Publication No. 2-266617. In this publication, the reception intensity of an electric wave sent from a base station is detected and when the reception intensity is smaller than a first threshold it is judged that the receiver is placed outside of an area where the electric wave can be received while when the reception intensity is larger than the first threshold but smaller than a second threshold it is judged that the receiver is placed within the area but can not receive the electric wave exactly with reliability.
In the above method, since judgment is made on the basis of the intensity of the received electric wave, the interference condition or the reception condition of the electric wave is different depending on circumstances of a building or the like even if the receiver is placed within the area and accordingly it is difficult to set the threshold.